Arrangement for producing a triggering effect in proximity to an object adapted to radiate radiantwave energy



May 4, 1948. PAGE 2,441,030 ARRANGEMENT FOR PRQDUCING A TRIGGERING EFFECT m PROXIMITY TO AN OBJECT ADAPTED TO RADIATE RADIANT-WAVE ENERGY Filed Jan. 3, 1941 Time FIG. I.

FIGQ4.

Time= FIG. 3;

Frequency.

' INVENTOR ARRY 6. PAGE ATTORNEY Patented May 4, 1948 ARRANGEMENT FOR PRODUCING A TRIG- GERING EFFECT IN PROXIMITY TO AN OBJECT ADAPTED T RADIATE RADIANT- WAVE ENERGY Harry 0. Page, Scarsdale, N. Y., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application January 3, 1941, Serial No. 372,988

12 Claims. (Cl. 102-703) This invention relates to arrangements for ex.- ploding projectiles in proximity to sound-emitting targets and, while the invention is of general utility, it is particularly adapted for use in anti-aircraft projectiles.

It is customary, when utilizing explosive shells against aircraft, to estimate the height of the target and to adjust a timing device in the projectile to cause the projectile to explode at the desired altitude. However, many factors combine to make this system of firing very difficult and inaccurate and to cause the percentage of hits to be very much less than desired. For example,.the following factors contribute to inaccurate results:

(1) Inaccuracies in estimating the range of the target;

(2) Inaccuracies in the timing arrangement of tion taken in connection with the accompany1n8 drawing and its scope will be pointed out in the appended claims.

the projectile which cause the detonation to be at an undesired point even though the range is correctly estimated; and

(3) Changes in range of the target aircraft after the firing data is computed.

It is very desirable, therefore, to provide a projectile-exploding device which is not subject to these disadvantages. For instance, it is desirable to provide an arrangement by which the explosion takes place as the projectile passes the point in its trajectory closest to the target.

It is an object of the invention, therefore, to provide an improved projectile-exploding device.

It is a further object of the invention to provide an arrangement of the type under consideration which is not subject to one or more of the disadvantages of prior art arrangements mentioned above.

It is a further object of the invention to provide an arrangement for exploding a projectile in the proximity of a sound-emittin target which requires no adjustment prior to the time of fir- In accordance with the invention, an arrangement for producing a triggering efl'ect in proximity to an object adapted to radiate radiantwave energy comprises means for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the energy radiated by the object, the means and the object having relative motion toward one another, and means responsive primarily to the change of frequency of the control effect produced as the means and the object pass one another at their closest point of approach for producing a second control efiect. The arrange- Fig. 1 of the accompanying drawing is a cincuit diagram, partly schematic, of a projectile= exploding device in accordance with the invention; while Figs. 2-5, inclusive, comprise graphs utilized to illustrate certain of the operating characteristics of the arrangement of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, the various parts thereof comprise an arrangement for producing a, triggering effect in proximity to a solind-emitting source. This arrangement, for example, is adapted to be included in a projectile to be exploded in proximity to a sound-emitting target and will be described in that connection. The unit In constitutes a means for generating a. periodic control effect varying in accordance with the characteristic frequency of the sound produced by the target or like source, for example, by the motor of thetarget aircraft where the arrangement is utilized in anti-aircraft projectiles. The unit l0 includes a microphone I I, having included in circuit therewith a battery 12 and a load impedance such as resistor [3, the microphone ll preferably being adapted to be mounted in the nose of the projectile. There are also coupled in cascade with the unit ID; a vacuum-tube amplifier and limiter M, a frequency-responsive circuit it, an amplitude detector IS, a difi'erentiatingcircuit I1, and a detonator l8. which is responsive to the triggering efi'ect produced by the arrangement for exploding the projectile. v

The amplifier and limiter EB may be ofconventional design and, as illustrated, includes a vacuum tube 20, having input electrodes coupled to the output circuit of unit In through a suitable coupling condenser 2| and grid-leak resistor 22. The output circuit of tube 20 comprises a load resistor 23,- while suitable operating p tentials are adapted to be applied to the screen electrode of tube 20 through resistor 24 and to the anode electrode of tube 20 through resistor 23 from a source of unidirectional operating potential +3. A condenser 25 is provided for by-passing periodic currents in the screen circuit of thetube. The circuit of tube 20 is preferably designed so that both grid-circuit limiting and anode-circuit limiting are efiected, the unidirectional operating potentials supplied to the tube being reduced to a suitable value to effect anode-circuit limiting and the elements 2| and 22 being so proportioned as to effect grid-circuit limiting.

The frequency-responsive circuit l5 may be of any desired type and, as shown, includes a blocking condenser 28, a series resistor 29, and shunt condenser 30. Detector I6 also may be of any desired type and, as shown, includes a diode 8| connected across the output terminals of unit I5,

that is, across condenser 30, together with a suitable parallel load resistor 32. The differentiating circuit I1 includes a condenser 84 in series in the signal-translating channel and a resistor 35 in shunt therewith. Detonator [8 includes input terminals adapted to be coupled across resistor 35 and is shown in block form for the rea-- son that the unit, per se, forms no part. of the seen that microphone II is adapted to respond to the sound produced by the sound-emitting target and thus to develop a control effect vary-- ing in accordance with such sounds, for example an alternating current having a frequency corresponding to the characteristic frequency of the sound emitted by the target and having amplitudes varying in accordance with the sound amplitudes. This current flows in the circuit including battery I2 and load impedance 13 to develop across the latter a signal potential. Furthermore, it will be seen that the characteristic frequency of such sound undergoes a sudden drop when the projectile passes the point in its trajectory closest to the sound-emitting target. This sudden'change in frequency is caused by the phenomenon well known as the Doppler" effect, which is the phenomenon which causes the apparent sudden change of pitch of a locomotive whistle when passing at a high rate of speed.

Due to the fact that the position of the projectile is rapidly varying with respect to the target, the sound received by the microphone ll correspondingly undergoes rapid variations of amplitude. Consequently, the amplitude of the signal enerated across load resistor is will also vary and limiter-amplifier it is provided for andplifying the signal generated across resistor it and for at least partially removing such amplitude variations. The amplitude of the translated signal is limited in one direction in tube 2% by rid-circuit limiting due to reduction of the gridcathode voltage by the grid-cathode current and is limited in the other direction by anode-circuit limiting due to the anode-current cutoff characteristic of the tube.

The frequency of the constant-amplitude signal output of limiter-amplifier it, varies, as previously pointed out, with the characteristic frequency of the received sound and thus varies in accordance with the curve of Fig. 2; that is, the frequency is substantially constant at the frequency f1 until the time 131 when the projectile is in the immediate vicinity of the point in its trajectory closest to the target. As the projectile passes the target, the frequency drops, due to the Doppler effect previously mentioned, thus reducing the characteristic frequency of the sound impressed on the microphone i i with consequent corresponding reduction of the frequency of the alternating current derived by the microphone it from the sound, for example during the time t1tz it drops to the value is of Fig. 2. The arrangement of the invention is adapted to be responsive to this sudden change in frequency to explode the projectile.

The frequency-response characteristic of the circuit i5 is illustrated in Fig. 3 of the drawing and the constants of the circuit elements are so proportioned that a decidedly drooping response characteristic .is provided over the frequency range 12-41. The frequency-responsive circuit i5 is designed so that the frequency range 11-42 includes all of therange of variation of the characteristic frequencies usually' encountered in sound emitted by targets for which the projectile is intended. The effect of translating the constant-amplitude signal output of unit l4 through the frequency-responsive circuit I5 is, therefore, to provide an output signal which varies in amplitude during the time interval when the projectile is passing the target, as indicated by the curve of Fig. 4. That is, the frequency of the signal input to circuit l5 has the fi value until the projectile passes fairly close to the target aircraft with the result that the signal output of circuit I5 has a low value of amplitude, as indicated in Fig. 3 by the low value of amplitude for this frequency; however, as the projectile passes the target, the frequency of the signal applied to the circuit l5 rapidly decreases to the value I:

with the result, as indicated in Fig. 3 by the rapid increase of amplitude between the frequencies 11 and Is, 'that the signal output of the circuit l5 rapidly increases in amplitude during the time t :tz to a fairly high value. The signal output of the circuit I5 is applied to the detector l6 where the signal is rectified to derive across the resistor 32 a unidirectional potential varying in amplitude with the amplitude of the signal output of circuit IS. The amplitude of the unidirectional signal output derived from detector l6 thus also varies in substantially the manner illustrated in the curve of Fig. 4. v

The differentiating device I! is effective to derive from the unidirectional signal input thereto a pulse voltage having instantaneous amplitude values which are the corresponding differential of the signal of Fig. 4; that is, a voltage having relatively low or substantially zero amplitude .until the time ti when the voltage amplitude suddenly increases'to a high value during the rapid change of amplitude of the unidirectional signal applied to unit if and thereafter suddenly decreases to a relatively low or substantially zero value at the time in. This voltage pulse is illustrated by the curve of Fig. 5 and is utilized to detonate the projectile.

In summary, therefore, it will be seen that the arrangement of Fig. 1 is one for producing a triggering effect in proximity to a sound-emitting source, as for exploding a projectile in proximity to a sound-emitting target. The arrangement comprises the unit it adapted to be mounted in the projectile for generating a periodic electrical control effect, specifically a signal potential, the frequency of which varies in accordance with the frequency of the sound produced by the source or target. The units M, M, and 56 comprise means responsive substantially only to the change of frequency, which change is essentially a rapid reduction of frequency, of the above-mentioned control effect, produced as the unit Ill in the projectile and the sound source or target pass one another at their closest point of approach, for producing a second electrical control effect, specifically a unidirectional control signal. The unit M comprises an amplifier and amplitude-limiter and the unit l5 comprises a frequency-responsive circuit. The unit I! comprises a means for differentiating the above-mentioned second control effect to derive a third control effect or triggering effect, specifically a pulse voltage, dependent upon the rate of change of amplitude thereof and,

therefore, dependent on the apparent rate of change of frequency of the received sound signal, while detonator 18 comprises means for utilizing the third control efiect to explode the projectile, the detonator is being thus indirectly responsive to the second control effect.

From a consideration of the operating characteristics of the system described above, it will be seen that no setting for altitude is needed prior to the firing of the projectile. Furthermore, it will be seen that the detonation of the projectile depends upon a high rate of change of frequency which can only take place during the time when the projectile is passing in close proximity to the target aircraft. In other words, the passing of the projectile through a plane normal to its trajectory and including the aircraft target is effective to produce the sudden pulse voltage of the wave form of Fig. 5, which pulse voltage is utilized for detonation. It is seen, therefore, that within very wide limits the production of this pulse voltage for actuating detonator I8 is not critical with relation to either-the speed of operation of the target aircraft's engine, and thus the absolute frequency of the sound, or to the speed of the projectile.

Furthermore, it will be understood that, since the arrangement of the invention need only operate for a few seconds, the various sources of potential required in the circuit can be of very short life, it being understood that the various elements of the circuit must be designed to withstand the shock incident to the firing of the pro- 1 jectile. The tubes utilized can, of course, be very small and, if desired, the tubes may be included within a single envelope. Also, it will be seen that, inasmuch as the detonating circuit is entirely electrical, the arrangement can be very fastacting, thus causing the projectile to explode in a predetermined relation to the point in its trajectory closest to the target. Inasmuch as this position of detonating is ensured by the arrangement of the invention, it may be preferable to design the projectile so that the principal burst of shrapnel from the Projectile is confined within predetermined limits. In this way, a considerable saving of space may be effected in the projectile to compensate for the space which is required for the detonating arrangement of the invention.

Also, it will be understood that the arrangement of the invention is particularlysuitable for use in fighter aircraft for the reason that it is unnecessary to perform an adjustment upon the projectile before firing in order to ensure its explosion at the proper range.

It may be found desirable to design the unit ll so that it is primarily responsive only to relatively low frequencies. In this way, the effect of the high-frequency noise generated by the projectile itself can be minimized. It may be desirable also to include a low-pass filter between the units i0 and I4 for the same purpose. Furthermore, it will be'understood that additional stages of amplification can be provided if desired.

While the term characteristic frequency" of the sound source or target is used in the foregoing specification and in the accompanying claims, it is to be understood that this term is intended to include the predominant frequency or frequencies of the sound which contain the major portion of the sound energy and which enable any given sound to be distinguished by the human ear from another sound. In general, any given sound source emits sound waves having one or more predominant or "characteristic frequencies together with a large number of other frequencies of low energy content. The predominant or character? istic frequencies of the sound generally lie relatively closely to each other in the frequency spectrum and enable it to be said that the sound has a characteristic high, medium or low pitch. It is the simultaneous change in the frequency spectrum of these predominant or characteristic frequencies of a sound resulting from the "Doppler" effect that enables one to say that a locomotive whistle, for example, appears to change pitch as the locomotive passes an observer. In the arrangement described, the frequency-response range 11 to ,fz of unit If: is materially broader than the range of predominant or characteristic frequencies comprising the sound received by the microphone ll of unit I! and thus may include such frequencies both before and after any shift thereof in the frequency spectrum such as caused by the Doppler" eflect.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An arrangement for exploding a projectile in proximity to a sound-emitting target comprising, means adapted to be mounted in the projectile for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the sound produced by said target, means responsive primarily to the change Of frequency of said control effect produced as said projectile passes the point in its trajectory closest to said target for producing a second control effect, and means for utilizing said second control effect to explode said projectile.

2. An arrangement for exploding a projectile in proximity to an energy-emitting target comprising, means adapted to be mounted in the projectile for generating a periodic electrical control effect the frequency of which varies in accordance with the characteristic frequency of the energy produced by said target, means comprising an amplifier and amplitude-limiter for translatlng' said generated control effect, means responsive primarily to the change of frequency of said translated control effect produced as said projectile passes the point in its trajectory closest to said target for producing a second control effeet, and means for utilizing said second control effect for exploding said projectile.

3. An arrangement for exploding a projectile in proximity to an energy-emitting target comprising, means adapted to be mounted in the projectile for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the energy produced by said target, means responsive primarily to the rate of change of frequency of said control effect produced as said projectile passes the point in its trajectory closest to said target for producing a second control effect, and means for utilizing said second control effect to explode said prising, means adapted to be mounted in the projectile for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the energy emitted by said target, an amplitude-limiter for deriving from said control effect a periodic wave of substantially constant amplitude, a primarily frequency-responsive circuit for deriving from said periodic wave a second periodic wave having an amplitude varying in accordance with the frequency of the energy emitted by said target, means for rectifying said second periodic wave, means for differentiating the output of said rectifying means to derive a pulse, and means for utilizing said pulse to explode said projectile.

5. An arrangement for producing a triggering effect in proximity to a sound-emitting source comprising, means for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the sound emitted by said source, said means and said source having relative movement toward one another, means responsive primarily to the change of frequency of said control effect produced as said means and said source pass one another at their closest point of approach for producing a second control effect, and means for utilizing said second control effect to produce said triggering effect.

6. An arrangement for producing a triggering effect in proximity to an object adapted to radiate radiant-wave energy comprising, means for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of the energy radiated by said object, said means and said object having relative movement toward one another, means responsive primarily to the change of frequency effect to produce said triggering effect.

7. An arrangement for producing a triggerin effect in proximity to an object adapted to radiate radiant-wave energy comprising, means responsive to received energy radiated by said object for generating a periodic electrical wave the frequency of which varies in accordance with the characteristic frequency of said received energy, said means and said object having relative movement toward one another, means responsive primarily to the change of frequency of said periodic wave produced as said means and said object pass one another at their closest point of approach for producing a control effect, and means for utilizing said control effect to produce said triggering effect.

8. An arrangement for producing a triggering effect in proximity to an object adapted to radiate radiant-wave energy comprising, means responsive to received energy radiated by said object for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of said received energy, said means and said object having relative movement toward one another, means responsive primarily to the change of frequency of said control effect produced as said means and said object pass one another at their closest point of approach for producing an electrical second control effect, and means for utilizing said electrical control efiect to produce said triggering effect.

9. An arrangement for producing a triggering effect in proximity to an object adapted to radiate radiant-wave energy comprising, means responsive to received energy radiated by said ob- Ject for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of said received energy, said means and said object having relative movement toward one another, means responsive substantially only to the change of frequency of said control effect produced as said means and said object pass one another at their closest point of approach for producing a second control effect, and means for utilizing said second control effect toproduce said triggering effect.

10. An arrangement for producing a triggering effect in proximity to an object adapted to radiate radiantwave energy comprising, means responsive to received energy radiated by said object for generating a periodic control effect the frequency of which varies in accordance with the characteristic frequency of said received energy, said means and said object having relative movement toward one another, means responsive primarily to the change of frequency of said control effect produced as said means and said object pass one another at their closest point of approach for producing a second control effect. means for differentiating said second control-effect to derive a third control effect, and means for utilizing said third control effect to produce said triggering effect.

11. In a device for detecting passage of an object producing sound of characteristic pitch, the combination of means associated with said device for receiving such sound and translating the sound energy into electrical energy of a frequency substantially proportional to such pitch as increased by the effect of relative approach velocity between said object and said means, output means, and means associated with said device for actuating said output means, said actuating means being responsive only to a reduction of frequency of such electrical energy corresponding to the reduction in received sound pitch occurring upon close passage of either said object or said receiving means by the other.

' 12. A control device responsive to the reduction of received sound frequency resulting from close relative passage at substantial speed between the device and a source of sound of characteristic frequency, including a microphone, an amplifier having its input connected to the microphone, a frequency-selective network connected to the output of said amplifier to provide output change from the network responsive to rapid reduction in frequency of the amplifier output corresponding to such sound frequency reduction, and a work device operating responsive to such network output change.

HARRY C. PAGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

